A paper sheet has been conventionally used as a packaging material or a base material for a gummed tape or the like. Especially, in an application requiring a strength, a thread-inserted paper sheet reinforced with a reinforcing thread is used.
For example, conventionally known thread-reinforced paper sheets used as a packaging paper sheet suitable for use, for example, in wrapping of a steel and as a fiber packaging bag, include those comprising upper and lower paper layers formed of a kraft paper or the like, and a reinforcing thread of glass, vinylon or the like interposed between the upper and lower paper layers.
In addition, conventionally known thread-reinforced gummed tapes include those having a moisture activated adhesive layer provided on one of surfaces of a tape base material which comprises an upper paper layer formed of, for example, "Clupak" paper, a lower paper layer formed of a kraft paper, and a reinforcing thread of glass, polyester, vinylon, nylon or the like interposed between the upper and lower paper layers.
However, the above prior art thread-reinforced paper sheet is accompanied by the following disadvantage: When the paper sheet is to be disintegrated with an aqueous alkali solution for regeneration, the upper and lower paper layers can be disintegrated without any problem, because they are soluble in water. However, both of an atactic polyolefin-based adhesive commonly used for laminating the upper and lower paper layers together and the reinforcing thread cannot be satisfactorily disintegrated. For this reason, when the used thread-reinforced paper sheet is to be regenerated, it is necessary to remove the reinforcing thread, resulting in a troublesome regenerating operation.
On the other hand, the above prior art thread-reinforced gummed tape is also accompanied by the following disadvantage: When the gummed tape is to be disintegrated with an aqueous alkali solution, the upper and lower paper layers constituting the tape base material and the moisture activated adhesive layer can be disintegrated without any problem, because they are soluble in water. However, both of a vinyl acetate emulsion-based adhesive commonly used for laminating the upper and lower paper layers and the reinforcing thread cannot satisfactorily disintegrated. For this reason, when a corrugated fibreboard case sealed using the thread-reinforced gummed tape or the like is to be regenerated, it is necessary to remove the gummed tape individually, resulting in a troublesome regenerating operation.
Thereupon, it is desired to propose a thread-reinforced paper sheet and a thread-reinforced gummed tape which are capable of being regenerated, as are a paper sheet and a gummed tape which are not reinforced with a reinforcing thread.
Accordingly, it is an object of the present invention to provide a regeneratable thread-reinforced paper sheet and a regeneratable thread-reinforced gummed tape to meet such demand.